SpaceX Falcon 9 successfully launches third set of Iridium-NEXT satellites

A SpaceX Falcon 9 rocket launched from Vandenberg Air Force Base Monday, before succcessfully deploying the third batch of ten Iridium-NEXT communications satellites into low Earth orbit. Liftoff from SLC-4E occurred on schedule during an instantaneous launch opportunity at 05:37 local time (12:37 UTC), with the booster successfully returning to the drone ship.

Iridium uses a large constellation of spacecraft in low Earth orbit to provide mobile satellite communications worldwide. The first-generation constellation was developed by Iridium SSC, a company financially backed by Motorola.

The original constellation was launched between 1997 and 2002. Iridium originally planned a 77-satellite constellation – with its name coming from the chemical element with atomic number 77. However, this was scaled back to 66 satellites, operating in six planes of eleven spacecraft each.

Iridium’s first-generation satellites were designed to operate for seven years. However, some of the spacecraft have been in operation for over twenty years, and the youngest satellites have been on orbit for over fifteen.

Of the ninety-five satellites launched, 60 were deployed in groups of five by Delta II rockets flying from Vandenberg Air Force Base, 21 were carried in three groups of seven aboard Proton-K/Blok-DM2 rockets flying from the Baikonur Cosmodrome, six pairs were launched by Chang Zheng 2C/SD vehicles flying from China’s Taiyuan Satellite Launch Centre and a further pair was launched aboard a Rokot/Briz-KM from the Plesetsk Cosmodrome. The Rokot launch, in June 2002, was the final replenishment mission for the original constellation.

By using satellites in low Earth orbit, Iridium expected to be able to offer its customers less latency than geostationary satellite communications, while eliminating the need for them to carry a large antenna to communicate with the satellite. The downside of this model was the larger number of satellites that would be needed to provide continuous coverage, and that all of these spacecraft would need to be in orbit before the company could begin providing the service to its customers.

The high setup cost of its constellation – estimated at around five billion dollars – operating costs and a slower-than-expected customer uptake led to Iridium filing for bankruptcy in 1999, less than a year after its service became operational.

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Faced with closure – and the deorbit of its fleet – the company’s assets and satellites were sold to a new company, Iridium Satellite LLC, in 2001 for around 25 million dollars. Since renamed Iridium Communications, this company has made the constellation successful and now aims to safeguard that success via a three-billion-dollar program to replace its entire satellite fleet.

Iridium selected Thales Alenia Space as the prime contractor for the second-generation constellation, named Iridium-NEXT. Eighty-one spacecraft have been ordered, based around Thales’ EliTeBus-1000, or Extended Lifetime Bus, platform.

This bus, derived from the earlier Proteus bus, gives the satellites a design life of ten years – although Iridium expects to be able to operate the new satellites for at least fifteen years. The order of eighty-one satellites covers the operational constellation, in-orbit spares and ground spares that can be launched at a later date as necessary.

Final assembly of the satellites is being undertaken in the United States by Orbital ATK. Each Iridium-NEXT spacecraft has a mass of 860 kilograms (1,900 lb). The satellites’ communications systems use L-band frequencies to transmit and receive data from customers’ handsets, and Ka-band transponders for communications to fixed ground stations and other satellites in the constellation.

The crosslink capability that the Ka-band payload provides – each satellite can relay transmissions to the spacecraft ahead of and behind it in the same plane, and to satellites in adjacent planes – allow calls to be routed worldwide without having to hand-off the signal to stations on the ground. This reduces the latency of customers’ calls.

Iridium has allocated 54 kilograms (120 lb) of mass and 90-200 watts of power per satellite to host payloads for other organizations. All of the Iridium-NEXT satellites carry Automatic Dependent Surveillance Broadcast (ADS-B) receivers for Aireon LLC, a partnership between Iridium and the government of Canada aimed at establishing a worldwide system to monitor air traffic. Over 60 satellites also carry exactView-RT payloads for exactEarth. The exactView payloads use an Automated Identification System (AIS) receiver to collect and relay tracking information from ships.

The ten spacecraft aboard Monday’s launch are Satellite Vehicles (SV) 107, 119, 122, 125, 127, 129, 132, 133, 136 and 139. SV-127 was originally built as SV-100, but was later redesignated.

Iridium has contracted SpaceX to launch seventy-five of the Iridium-NEXT spacecraft via its Falcon 9 rocket. The first launches under this contract were conducted earlier this year: Falcon missions in January and June have deployed twenty satellites into orbit. Another launch is expected later this year, with three more in the opening months of next year bringing the constellation up to seventy satellites.

A further launch, currently scheduled for next March, will carry five additional Iridium spacecraft and the two GRACE Follow-On geodesy spacecraft for NASA and Germany’s DLR.

The pad was used initially by Atlas SLV-3 Agena-D rockets, and later by Titan vehicles: the Titan III(23)D, Titan III(34)D and Titan IV. The final launch of the Titan family of rockets was made from SLC-4E in October 2005, by a Titan IV(404)B. Twenty-Seven Atlas and forty-one Titan rockets launched from the pad.

SpaceX has since leased SLC-4E from the US Air Force, demolishing the former Titan launch facilities in 2011 ahead of the first Falcon 9 launch from Vandenberg in September 2013. SpaceX has also leased the launch complex’s other pad, SLC-4W, which they are converting for use as a landing pad for first stage recovery operations. Monday’s is the sixth launch that SpaceX has made from SLC-4E and the seventy-second overall from the launch pad.

Nine Merlin-1D engines power Falcon 9’s first stage, attached in an octagonal, or OctaWeb, arrangement at the base of the stage. Each first stage, or core, is designed to be used for multiple launches and is capable of flying back to Earth – either to the launch site or a barge (Autonomous Spaceport Drone Ship or ASDS) downrange depending on the requirements of individual missions. Falcon 9 is the only rocket apart from the Space Shuttle to have demonstrated reusability.

The first stage that powered Monday’s mission was Core 1041, a new core which is making its first flight. Following a nominal countdown, the core’s nine engines ignited three seconds before the clock reaches zero. At zero, Falcon 9 began her climb away from the launch pad. About seventy seconds after liftoff, Falcon reached the point of maximum dynamic pressure, or max-Q, when aerodynamic loads on the vehicle are at their greatest.

Falcon’s first stage burned for the first 143 seconds of flight before shutting down its engines, an event designated main engine cutoff, or MECO. Four seconds after MECO, the first and second stages separated with the second stage continuing towards orbit with the payload, while the first stage began its descent back to Earth for recovery and potential reuse.

The second stage ignited its single vacuum-optimised Merlin-1D engine six seconds after staging, beginning the first of two planned second stage burns.

The first burn of the upper stage lasted six minutes and 25 seconds, with separation of the rocket’s payload fairing occurring 39 seconds into the burn. While the second stage burn was ongoing, the first stage made a series of maneuvers culminating in a landing aboard the Autonomous Spaceport Drone Ship (ASDS) Just Read the Instructions in the Pacific Ocean.

As soon as the first stage separates, it reoriented itself for the return journey. Thirteen seconds after separation, the stage fired three of its engines in a boostback burn, changing its course so it flew back towards the ASDS, waiting off the California coast. With the boostback complete, the core deployed its gridfins, devices that help to steady and guide its course as it falls back through the atmosphere.

Three minutes and 14 after stage separation, the first stage restarted for an entry burn, firing three engines to slow its descent as it began to pass back into the denser regions of Earth’s atmosphere. Landing occurred about 82 seconds later, with the stage igniting a single engine shortly beforehand to arrest its descent and guide itself to a controlled touchdown on the deck of the drone ship.

About 98 seconds after the first stage lands, the second stage concluded its first burn, shutting down is engine in an event designated SECO-1, or second stage engine cutoff 1. The rocket coasted for 43 minutes and one second before the stage made its short second burn, lasting just three seconds before SECO-2. Separation of the ten satellites began five minutes and one second after cutoff, with the process lasting five minutes. After the last satellite separated, Falcon 9’s first stage will be deorbited.

The fourteenth launch of the year for SpaceX, Monday’s mission will be followed by another Falcon 9 launch from Florida’s Kennedy Space Center on Wednesday. The next launch, which will involve a flight-proven first stage, will carry the EchoStar-105/SES-10 communications satellite to geostationary transfer orbit for EchoStar and SES. Falcon’s next mission from the West Coast, and the next launch for Iridium, is currently scheduled to lift off no earlier than November.